Several posts on other forums have suggested Internet proof of Vitamin B1 as a bug (Sand Flea) repellent.
I’ll post what I found.
The bugs we encounter tend to feed at different times of the day.
Sand fleas feed on romantic Canadians who like to stroll on the beach barefoot after sundown when the fleas come out to find a warm meal. Fleas don’t like hot sand and stay burred during the day.
People post these awful photos of their lower legs and swear the bites are from mosquito, midges or bed bugs.

A good test to see if you have sand flea bites is to try an anti itch “stick”. One of those ammonia applicators that reduce the itch of bug bites. If the “itch stick” works, it’s a mosquito bite; if it doesn’t, it’s a flea bite.
If it stays with you for months and is itchy as hell, it’s a sand flea bite.

B1? maybe not?
I followed the Google thread and at the end I found this:
"Preventing insect bites and stings
When out and about
Bites and stings most commonly occur when outside, particularly in the countryside. Ways to avoid bites and stings include:
Wear long sleeved clothing and long trousers in places where insects are common.
Avoid brightly coloured clothes, cosmetics, perfumes or hair sprays, which attract insects.
Rub an insect repellent onto exposed areas of skin.
Be alert when you cook or eat outdoors as food attracts insects, especially wasps.
Some people wear a complete head covering with a plastic viewer when out where midges are common. For example, when camping next to lakes and rivers. Many camping shops sell them.There is no evidence that eating garlic, vitamin B1 or other foods will repel insects."

I never have been bothered by sand fleas or anything else while away. I did however try B complex, supposed to be a wonderful way to keep black flies, skitters etc off us here in the wet Canadian spring and summers.

Didn’t do a thing for me. I got bitten just as much as I ever did. Took the B complex for about 2 months prior to the season and all summer long.

I think if your going to get bitten you will. The love some more than others. I have seen some of the pictures that have been posted. One that stands out was last year at the Melia Las Dunas. They said it was bed bugs…I was doubtful as they were only on the lower limbs. I could be wrong but it sure looked like sand flea bites to me. I have been with other who have had the same reaction.

As a Certified Natural Products Advisor and a Certified Herbalist, I can tell you that B vitamins will not help. Also, the more carbs you eat, the more the bugs will like you. I have found that Quantum Buzz Away applied liberally works much better than DEET products. And Boiron Apisgel takes away the itching, swelling and redness very nicely if you do get eaten alive. Myself, I can reduce the bites but never avoid them totally. My husband hardly gets bitten at all. He has oily, Meditarannean skin and I wonder if that’s a factor. I’m a total WASP.

First of all, if one more old hippy tries to sell me the urban myth that some B1 and garlic pills will make anyone impervious to all bugs I’ll scream. What a load of crap. Since you’re a pro Sadcdn it’s good to hear you also dispel this old wish-it-were-true tale.

Regarding repellent, I’ve spend a fair amount of time in really bad malaria areas and since bugs love me I’ve tried everything under the sun to protect myself. The Buzz Away by Quantum and Herbal Armor by All Terrain are definitely the best of the DEET free products, but (for me at least) they can’t hold a candle to DEET. I wish it wasn’t true.

I’ve only been nailed by sand fleas once in Cuba and it’s an experience I never want to repeat. No more romantic walks on the beach for me when those little monsters are feeding…

On our last trip to Cuba, I was determined to take anything and everything I had read that may work on bite - the mozzies love me!
I took a combination of B1 and Garlic, started about 30 days prior to leaving. I teamed that up with Avon Skin So Soft, and despite what others say - it worked. Not sure what component fended them off, could have been the SSS, on its own but I will definately take it all again this fall.

I agree with Tigs - I used to get bitten really badly - you could play ‘dot to dot’ on my legs and I would end up have to take a course of antihistamine on return from my hols. These days when on hol I use only Avon Skin So Soft to wash with and as an after sun and moisturiser - no perfume etc. I also take Vit B1 prior to holiday for about 3 weeks and now I claim I’m unlucky if I get 1 small bite. This has worked in Mexico, Dominican Republic and Cuba! My husband Pooh poohs this and he is the one who now gets bitten he he!

I agree too with tigs and cherryfan. In the past I have been bitten so badly (100) and it didn’t seem to matter if I was on the beach or by the pool (both times were Cayo Coco area) so I gave the Vit. B1 a try. It could be because of the different areas of Cuba we are staying at where there is no sand flea activities however it seems to work. I have had no bites unless it is a few mossie bites and those I can live with.